Octupole Correlations in Positive-Parity States of the Rare Earths and Actinides

Transcription

1 Octupole Correlations in Positive-Parity States of the Rare Earths and Actinides Mark Spieker 1,*, Dorel Bucurescu 2, Janis Endres 1, Thomas Faestermann 3, Ralf Hertenberger 4, Sorin Pascu 1,2, Hans-Friedrich Wirth 4, Nicolae-Victor Zamfir 2, and Andreas Zilges 1 1 Institute for Nuclear Physics, University of Cologne, Germany 2 Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania 3 Physik Department, Technische Universität München, Germany 4 Fakultät für Physik, Ludwig-Maximilians-Universität München, Germany CGS 2014 Dresden (Germany) Supported by the DFG (ZI 510/4-2) *Supported by the Bonn-Cologne Graduate School of Physics and Astronomy M. Spieker, University of Cologne, AG Zilges Octupole Correlations in Rare-Earth and Actinide Nuclei

2 Octupole Correlations in Atomic Nuclei P. Cottle, Nature 465 (2010) 430 Rare Earths: 146 Nd Actinides: 240 Pu Dj, Dl= 3 Dj, Dl= 3 Dj, Dl= 3 Octupole driving numbers: 34, 56, 88, 134 Dj, Dl= 3 P.A. Butler, W. Nazarewicz, Rev. Mod. Phys. 68 (1996) 349

3 Alternating-Parity Bands in the Actinides Theory Experiment L.P. Gaffney, P.A. Butler et al., Nature 497 (2013) 199 S. Frauendorf, PRC 77 (2008) (R) E1 Transitions T(E1) D 0 b 2 b 3 Static octupole deformation in 224 Ra Talk by M. Scheck, Session 29, Fr, 11:30 F. Iachello, PLB 160 (1985) 1

4 Octupole Correlations in 240 Pu 240 Gammasphere, Argonne National Laboratory Experiment Build-up of an alternating-parity band at J 20 Induced intrinsic dipole moment D 0 = 0.2 efm (e.g. light Thisotopes efm) g.s.b. K p = 0 - X. Wang et al., PRL 102 (2009) I. Wiedenhöver et al., PRL 83 (1999) 2143

5 Octupole Correlations in 240 Pu 240 Gammasphere, Argonne National Laboratory g.s.b. K p = 0 - X. Wang et al., PRL 102 (2009) I. Wiedenhöver et al., PRL 83 (1999) 2143 Experiment Build-up of an alternating-parity band at J 20 Induced intrinsic dipole moment D 0 = 0.2 efm (e.g. light Thisotopes efm) Octupole deformation might set in at high spin R.V. Jolos et al., PRC 86 (2012) S. Frauendorf, PRC 77 (2008) (R)

6 Octupole Correlations in 240 Pu 240 Gammasphere, Argonne National Laboratory Experiment Observation of an additional K p = 0 + rotational band up to highest spins Exclusive decay to K p = 0 - one-octupole phonon band Enhanced E1 transitions of 2 mw.u. K p =0 - Excited Kp =0 + X. Wang et al., PRL 102 (2009) I. Wiedenhöver et al., PRL 83 (1999) 2143

7 Octupole Correlations in 240 Pu 240 Gammasphere, Argonne National Laboratory Experiment Observation of an additional K p = 0 + rotational band up to highest spins Exclusive decay to K p = 0 - one-octupole phonon band Enhanced E1 transitions of 2 mw.u. K p =0 - Excited Kp =0 + Theory K p = is double-octupole phonon band X. Wang et al., PRL 102 (2009) I. Wiedenhöver et al., PRL 83 (1999) 2143

8 First Excited 0 + States in the Actinides Uniformly strong (p,t) population of first-excited 0 + states Collective excitation? J.V. Maher et al., PRL 25 (1970), 302; J.V. Maher et al., PRC 5 (1972), 1380; A.M. Friedman et al., PRC 9 (1974) 760

9 First Excited 0 + States in the Actinides Uniformly strong (p,t) population of first-excited 0 + states Collective excitation? 240 Pu J.V. Maher et al., PRL 25 (1970), 302; J.V. Maher et al., PRC 5 (1972), 1380; A.M. Friedman et al., PRC 9 (1974) 760

10 Experimental Setup Experiment: Two-neutron transfer reaction (p,t) to populate low-spin states in 240 Pu (E p = 24 MeV) MLL, Munich Particle-Energy Resolution: DE/E = (4 E t = 20 MeV) Spatial Resolution: 3.5 mm repetition length, 255 cathode strips (length: 1 m) Target: 120 mg/cm Pu (99.93%, T 1/2 = 3.75 x 10 5 a) on a 25 mg/cm 2 carbon backing (provided by Oak Ridge National Laboratory)

11 Excited States in 242 Pu(p,t) 240 Pu 2 magnetic settings of Q3D to cover the focal plane of 1.8 m Excitation energies up to 3 MeV could be measured Observation of 208 excited states (J p = ) Q3D = 10 Q3D = 10 Particle Spectrum M. Spieker et al., PRC 88 (2013) (R)

12 Experimental Results and IBM Calculations 19% 8% EXP Experiment 17 (21) J p =0 + states excited up to E x = 3 MeV Two firmly assigned 0 + states below 2D n 2 nd 0 + state 19% of g.s. transfer strength 22% 2D n 13% IBM spdf IBM theory 10 J p =0 + states with non-vanishing transfer strength predicted (12 in total) Two 0 + states below 2D n predicted 2 nd 0 + state 22% of g.s. transfer strength Conclusion Double-octupole structure predicted Two groups of excited states Correct prediction of transfer strength Stronger fragmentation observed M. Spieker et al., PRC 88 (2013) (R)

13 Octupole Correlations in Atomic Nuclei P. Cottle, Nature 465 (2010) 430 Rare Earths: 146 Nd Actinides: 240 Pu Dj, Dl= 3 Dj, Dl= 3 Dj, Dl= 3 Octupole driving numbers: 34, 56, 88, 134 Dj, Dl= 3 P.A. Butler, W. Nazarewicz, Rev. Mod. Phys. 68 (1996) 349

14 Octupole-Phonon Condensation [1] Synchronization of rotating quadrupole shape (w 2 ) and octupole wave (w 3 ) at w c Octupole-phonon condensation Rotating heart/pear shape [1] S. Frauendorf, PRC 77 (2008) (R) Signatures: Common tangent of E(J) for n-phonon bands n-phonon bands cross at w c

15 Octupole-Phonon Condensation in 146 Nd? w c M. Spieker et al., to be published Data compiled from ENSDF

16 Octupole-Phonon Condensation in 146 Nd? M. Spieker et al., to be published Data compiled from ENSDF

17 Octupole-Phonon Condensation in 146 Nd? Routhians in 146 Nd w c EXP EXP 2 2-octupole phonon band? 3-octupole phonon band? M. Spieker et al., to be published Data compiled from ENSDF

18 Multiphonon-Octupole Excitations in 146 Nd? Signature Splitting: M. Spieker et al., to be published Data compiled from ENSDF

19 Multiphonon-Octupole Excitations in 146 Nd? Signature Splitting: M. Spieker et al., to be published Data compiled from ENSDF

20 Multiphonon-Octupole Excitations in 146 Nd? Signature Splitting: M. Spieker et al., to be published Data compiled from ENSDF

21 Summary Experiment 242 Pu(p,t) 240 Q3D, MLL Munich 200 excited states observed 20 excited J p =0 + states up to 3 MeV 146 Nd Occurrence of additional p=+ and p=- bands (Routhians cross!) Change in Yrast structure Theory Double-octupole states predicted in IBM and other theoretical models Octupole structure essential to describe different experimental observables in rare earths and actinides, e.g., E1 strength, B(E1)/B(E2) ratios How do double-octupole states effect basic nuclear properties, e.g., octupole deformation, Yrast structure?

22 Outlook Cologne E1 E E2 0 + E Study of decay properties and lifetime measurements in particle-g coincidence experiments Gate on excitation energy in particle spectrum (SONIC) Decay of specific state can be studied selectively (HORUS) DSAM measurements possible with SONIC@HORUS Lifetimes can be determined without any feeding contributions due to selective gate on excited state